Bumping gaia.json for 4 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/a8720a418a85
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Merge pull request #14667 from mcav/utf7

Bug 938321 - [email/backend] Implement utf-7 charset support using hand-rolled decoder. r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/5037ab809d20
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Bug 938321 - [email/backend] Implement utf-7 charset support using hand-rolled decoder.

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https://hg.mozilla.org/integration/gaia-central/rev/f1fcc0bf2d28
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #14508 from julienw/942863-use-height-instead-of-border-bottom

Bug 942863 - Workaround for a Gecko bug in SMS app with APZ enabled. r=borja

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https://hg.mozilla.org/integration/gaia-central/rev/d3ac0ec93099
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 942863 - [SMS] The messages list content can not be scrolled to the end r=borja